The present invention relates to welding transformers and rectifiers, and more particularly to transformers and rectifiers for robotic welders.
In resistance welding, coalescence is produced primarily by resistive heat created by passing an electric current through the workpiece. A resistance welder includes primary conductors, a transformer, secondary conductors, and welding electrodes. The primary conductors couple the transformer to a power source. The secondary conductors interconnect the transformer and the electrodes.
Typically, the primary power source or supply in resistance welding provides power at the line frequency--for example, 60 hertz (Hz) in the United States and 50 Hz in Europe. Welding transformers for this relatively low-frequency current are excessively heavy for many robotic welders where weight is a primary consideration.
In an attempt to reduce the weight of the transformer, artisans have used relatively high-frequency power sources (e.g., 400 or 1200 Hz). By so boosting the frequency, the transformer weight can be greatly reduced. However, the increased frequency requires the secondary voltage to be increased because of increased inductive reactance, which is directly proportional to frequency. In an attempt to reduce impedance, artisans have rectified the secondary voltage/current. One such construction is illustrated in U.S. Pat. No. Re. 31,444, reissued Nov. 15, 1983, to Block, and entitled TWO-PHASE TRANSFORMER AND WELDING CIRCUIT THEREFOR. Such constructions are relatively bulky and heavy and therefore not fully adaptable to all robotic welders. Further, the shunts between the transformer and the rectifier are "inductive throats", such that the high-frequency reactance problem remains.